Significance If learning contributes to the development of vocal production in the squirrel monkey, then this will represent an important parallel between primate vocal development and human phonological development and may provide the first nonhuman primate model for studying language development in human children. Objectives The primary objective of this research is to determine the importance of learning in the acquisition of vocal skills in non-human primates. The specific aims are to document the development of vocal production of chuck calls in squirrel monkeys. The chuck call in squirrel monkeys is acoustically different in infants and adults, and is produced primarily by adult females during close affiliative interactions, which shows a strong degree of individuality in acoustic structure. Such characteristics suggest that learning may play an important role in the maturation of this vocal subsystem. Results Data analysis is currently in progress. Over 150 hours of vocal recordings and 400 hours of focal behavioral data have been collected. Results suggest that infant/juvenile squirrel monkeys show social preferences for particular unrelated adult females. Social preference was measured by the amount of time infants/juveniles spent in proximity, contact, and social huddling with different adult females, as well as in the amount and direction of activities such as approaches, social exploration and play, retrievals, and agonistic interactions. These data suggest that sufficient variation exist between infants in their social preferences to evaluate social influences on chuck call development. Over 3000 chuck calls already have been digitized for quantitative acoustic analysis. Preliminary comparison suggests that some acoustic features of chuck calls are learned by infants from unrelated close social associates. Future Directions A combination of advanced bioacoustic techniques and DNA fingerprinting methods will be used to determine the acoustic parameters that are learned from those that are more innately predisposed in squirrel monkey vocalizations. KEY WORDS vocal learning, language development, evolution of language, bioacoustic analysis FUNDING NIH NRSA Fellowship 1-F32-HD07946